In the drilling of subsea wells it is often desirable to support all casing strings at the mudline. This creates the problem of hanging a plurality of concentric strings of casing within one another from their respective hanger bodies. Since each hanger body and the supports therefore, must be run through a length of riser to reach the support elevation, there is a serious limitation on the annular space available to the supports to perform the required operations. The simple support arrangements available for surface wells are not available here.
U.S. Pat. No. 3,411,588 to J. W. E. Hanes illustrates the problem and one solution therefor. An internal circumferential slot is provided in a first casing hanger. The support ring is shaped having an inwardly extending support shoulder with the support ring being cut to form a so called C shaped member, and with this member being formed such that it naturally tends to spring outwardly into the slot.
The support ring is held in the contracted position, and lowered to a point slightly above the support elevation. It is thereafter released springing out against the inside surface of the riser. It is pushed down until it reaches and snaps into the annular groove in the hanger body. This provides the support ring for the next run casing hanger.
While the casing interior and support slot may be sprayed during running of the support ring, there is no assurance that all dirt or cement would be removed, and accordingly it is possible that the ring may not fully expand within the slot to provide a reliable support. It is also possible that it cock in such a way that it is actually recompressed when load is placed thereon, pushing it farther down the pipe rather than requiring it to stay in place and accept the load.